Rail transport is a very energy efficient means of freight and passenger transport. Compared to road transport using trucks, it consumes two to five times less energy. Train traffic is carefully and precisely planned by transportation engineers well in advance. There is an exact schedule for every train. However, this system is highly sensitive to any delays. To still allow for safe travel despite small changes or delays in the schedule of a train, railway transport uses a signaling traffic control system. Railway signaling provides traffic control to trains and thereby helps to prevent accidents. The signaling system uses a significant portion of the infrastructure cost: it comprises up to 10% of the infrastructure expenses in Europe.
The state of the art railway safety system, known as signaling, is based on a technology which goes back to the 19th century. The principle of signaling is the following: trains are given permission by means of signals to move into the blocks, i.e. segments of railway track into which the railway lines are divided. The fundamental traffic management approach is to ensure that two trains are not allowed to occupy the same block at the same time. While in the early 19th century signals were given by railway officers by means of hand signals, this very primitive signaling system has gradually evolved to the Communication-Based Train Control (CBTC) where trains communicate with track equipment by means of radio signals.
For each block, on the side of the rails, hardware has to be installed to detect the presence of a train. If such a block is occupied by a train, no other train is allowed to enter it and, hence, such a train would be shown a signal, for example a red light. In this case, the train would have to fully stop and wait until the block is cleared and the signaling system shows the green light.
A drawback of this system is the low accuracy of the estimation of the position of the train: as it cannot resolve whether a train is at the beginning of the block or at the end of the block. In any case, the train trying to come into the same block will have to wait until the block is free, which is very inefficient. One way of increasing the efficiency is reducing the length of the blocks. However, this would increase the cost considerably and it is limited by the maximum length a train may have.
There is a substantial improvement in the most recent signaling system, called CBTC. The position of the trains is more precisely estimated by means of GPS equipment aboard the trains. In the CBTC system, trains communicate with hardware installed next to the tracks known as balises. The trains communicate with the balises at 2.4 GHz. The communication range this high frequency can attain is not very large in comparison with lower frequencies. Therefore, there has to be a balise installed in the rail infrastructure every few hundred meters. Typical distances would be about 300-500 meters; although in some cases it is necessary to install them at shorter distances, such as 50 m, if the channel characteristics are not good enough. The balises are usually interconnected through fiber. This way, the information a balise receives from a train in its close vicinity is propagated to the rest of the balises, and these can transmit this information to the trains in their vicinity. Hence, the trains have a more accurate knowledge of the position of the preceding trains on the track. CBTC can use mobile blocks instead of fixed blocks. A mobile block is defined around the train and its speed is varied to assure that no mobile blocks overlap. Compared to the fixed block signaling system, CBTC is clearly more traffic efficient, but still requires the installation of trackside hardware.
Therefore, the state of the art infrastructure-based safety systems do not provide a scalable solution. The more kilometers of railway, the higher would be the cost of equipment for safety and traffic management. The higher the traffic volume the lines should handle, the higher is the cost of safety.
Another limitation of prior art railway traffic management systems is that despite the existence of this cost-intensive system, the probability of failure is not negligible, as hardware error or human error leads to travel past stop signals. Besides accidents, signaling failure leads to delay. Therefore, it is clear that there is a need for a completely new safety system that increases safety and efficiency while reducing infrastructure and maintenance costs.
Legislation passed by the US Congress in 2008 mandates that “positive train control” (PTC) be installed by the end of 2015 on U.S. Class I rail main lines used to transport passengers or toxic-by-inhalation (TIH) materials.
“Positive train control” describes technologies designed to automatically stop or slow a train before certain accidents caused by human error occur. Specifically, PTC as mandated by Congress must be designed to prevent train-to-train collisions; derailments caused by excessive speed; unauthorized incursions by trains onto sections of track where maintenance activities are taking place; and the movement of a train through a track switch left in the wrong position.
A functioning PTC system must be able to determine the location and speed of trains, warn train operators of potential problems, and take action if the operator does not respond to a warning. For example, if a train operator fails to stop a train at a stop signal or slow down for a speed-restricted area, the PTC system would apply the brakes automatically. This might sound simple, but to work properly it requires highly complex technologies and information processing capabilities and communications systems able to incorporate and analyze the huge number of variables that affect rail operations. A simple example: the length of time it takes to stop depends on the terrain, weight and length of the train, the type of braking technology on the train, and other factors. A PTC system must be able to take all of these factors into account reliably and accurately.
Railroad operators are committed to meeting the PTC mandate and are working hard to make it happen, but it will be an enormous technical and financial undertaking. According to the FRA, railroads will have to spend around $5 billion to install PTC. Railroad operators think that the $5 billion estimate is way too low—their best estimate to date is that installation will cost $5.8 billion for freight railroads and another $2.4 billion for passenger railroads. Everyone agrees that PTC will require hundreds of millions of dollars each year to maintain. In total, according to FRA estimates, PTC will cost railroads up to $13.2 billion to install and maintain over 20 years”.
In Europe, rail equipment manufacturers have developed over 20 signaling and speed-control systems, all of which are incompatible with each other. The European Commission has therefore called in 2005 for the gradual transition to a system that is common to the various EU member states: the European Rail Traffic Management System (ERTMS). This has two components:
(1) GSM-R, a radio communication system based on standard GSM (used by mobile telephones), but using various frequencies specific to rail;
(2) European Traffic Control System (ETCS), which not only allows permitted speed information to be transmitted to the driver, but also the driver compliance with these instructions.
GSM-R is built on GSM technology, and the benefits from the economies of scale of its GSM technology heritage, aiming at being a cost-efficient digital replacement for existing incompatible in-track cable and analog railway radio networks. GSM-R is part of the ERTMS standard and carries the signaling information directly to the train driver, enabling highest train speeds and traffic density with a high level of safety. GSM-R has been selected by 38 countries across the world, including all member states of the European Union (EU) and countries in Asia, Eurasia, and Northern Africa.
GSM-R is typically implemented using dedicated base station towers close to the railway. The distance between the base stations are 7-15 km. This creates a high degree of redundancy and higher availability and reliability. The train maintains a circuit switched digital modem connection to the train control center at all times. This modem operates with higher priority than normal users (eMLPP). If the modem connection is lost, the train will automatically stop. In Germany, Italy and France the GSM-R network has between 3000 and 4000 base stations. In Europe, GSM-R uses a specific frequency band:
876 MHz-880 MHz: used for data transmission (uplink)
921 MHz-925 MHz: used for data reception (downlink).
While the deployment of GSM-R, based on successful public GSM technology, is taking place quickly, ETCS has been developed specifically for the rail sector and will take longer. It requires the installation of a specific module on board the train and for the transducers on the track to use the same ETCS format. Given the long service life of rail equipment (more than 20 years), it is impossible to renovate the entire network at once. The Commission therefore estimates that it is inevitable that there will often be at least one system coexisting with ETCS on board and/or on the track.
The European Commission was planning a rapid migration strategy (within 10-12 years), with the aim of quickly reaching a critical mass of ETCS equipment. The entire rail sector also hopes that such a strategy can be implemented having endorsed a Memorandum of Understanding (MOU) on Mar. 17, 2005. In concrete terms, this entails investment amounting to $7 billion USD in order to reach the critical mass by 2016. In the current economic climate in Europe, it is very uncertain whether this goal can be reached by 2016.
ETCS enables ground-based equipment to transmit information to the train. This enables equipment on the trains to continuously calculate the maximum permitted speed. Information is transmitted by standardized beacons—Eurobalises—which are placed along the length of the track and connected to the existing signaling system. This is “ETCS Level 1” (ETCS-1). This technology is now mature, and Eurobalises can be purchased from several manufacturers.
In addition to ETCS-1, there are level 2 (ETCS-2) and level 3 (ETCS-3) systems as well. While the ETCS-2 and ETCS-3 systems do not use traffic lights on the sides of the rail tracks, they still use a centralized traffic control system in the form of a “Radio Block Center” which plays the role of a mediator between the trains (and onboard communications and computing equipment) and the sensors on the track (Eurobalises). Level 2 signaling system is an improvement over Level 1 in terms of efficiency and utilization. Level 3 (ETCS-3) holds the potential of having major benefits in terms of maintenance and operational capacity. Level 3 ETCS systems, however, are still at an experimental stage.